Gregorian Masses consist of 30 Holy Masses said in succession and without interruption for the deliverance of an individual soul from Purgatory to heaven.
According to legend, dating back to mid-sixth century, a deceased monk appeared and requested 30 Masses to be celebrated for the release of his soul from Purgatory. On completion of the stipulated number of days, he appeared once more radiant in heavenly glory.
These 30 Masses are called Gregorian Masses because Saint Gregory contributed to the spread of this pious practice. Saint Gregory, as we read of his life, was also instructed by God Himself in the efficacy of these 30 Masses and he recommended the practice on various occasions.